1. Field of the Invention
The present invention relates to lighting fixtures, particularly terrain lighting fixtures adapted for landscape lighting applications. The present invention also relates to lighting fixtures adapted for spatially moving between extended operating positions and retracted non-operating positions.
2. Background of the Invention
Terrain lighting is a type of exterior lighting where light fixtures are placed in close proximity to the ground and/or to vegetation. This particular type of outdoor lighting is popular with building and landscape architects because the nighttime play of light on landscape, vegetation, and artifacts such as buildings is aesthetically pleasing. This type of terrain lighting is especially popular in the southwestern or "sunbelt" states of the U.S. where decorative landscape lighting is used to support activities conducted out of doors because of favorable weather conditions.
Terrain landscape lighting fixtures, which generally protrude above the ground in order to perform their illumination function, are not generally perceived to be equally as aesthetically pleasing during hours of daylight as is the illumination which such fixtures provide during hours of darkness. The above-ground fixtures often appear incongruous with surrounding vegetation. They are generally required to be made of expensive and high-quality materials, typically non-corrosive metals such as aluminum alloys, so as to be reasonably durable and resistant to damage, and so as not to appear shabby. Accordingly, they look distinctly man-made and unnatural.
Terrain lighting fixtures placed anyplace in the landscape, and particularly within lawns adjacent a sidewalk or pathway, present objects over which a person may fall. The fixtures are subject to damage by irrigation watering, animals and vehicles. To resist damage they must present significant strength and resistance to the elements, which increases cost.
Maintenance of the landscape, such as by mowing, in the vicinity of terrain lighting fixtures is difficult. The vegetation or grass is normally trimmed in the region of such fixtures by use of hand shears or a string trimmer. This required trimming is a separate, time-consuming task to normal lawn mowing.
Because of these difficulties with standard terrain lighting fixtures, there has been at least one previous attempt to provide a terrain lighting fixture that retracts to an innocuous and safe position below ground during periods of non use, and which extends above ground during periods of use in order to light an adjacent landscape area. Such a RETRACTABLE LIGHT FIXTURE is taught in U.S. patent Ser. No. 4,180,850 to Bivens.
The retractable light fixture of Bivens is hydraulically operated for forcing a retractable member bearing a light bulb out of a buried housing when lighting is desired. The fixture must correspondingly be both plumbed, typically with water, and electrically wired. The necessity of plumbing a fixture with pressured fluid increases its installation cost. Each retractable light fixture is required to be able to retain fluid pressure, preferably without undue leakage, over a protracted period of time. The fluid must be reliably isolated from the electrical connections so that it does not cause destructive short circuits.
The retractable light fixtures of Bivens are actuated for preselected times and durations by use of an irrigation-type electrical controller or the like. Although a number of light fixtures within an area may be simultaneously enabled in response to a light-operated sensor, or else in response to manual actuation, the individual retractable light fixtures of Bivens are not individually actuable. Such individual actuation may be useful when different parts of the terrain under illumination become darker or lighter relatively earlier or later in the dawn and dusk diurnal cycles.
Accordingly, it would be desirable if the function of a retractable terrain lighting fixture could be realized in a lighting fixture that was relatively inexpensive to make, install and maintain relative to previous fixtures. Moreover, such a fixture would desirably permit discreet, local, control of one or more fixtures. For certain relatively inaccessible and/or highly visible locations where it is difficult even to wire, let alone plumb, a retractable light fixture, such a fixture might desirably be self-contained.
In another technical area, certain alloys of metals are known that exhibit what is called the shape-memory effect. If such alloys are plastically deformed at one temperature, they will completely recover their original shape upon being raised to a higher temperature. These higher temperatures can be induced by the conduction of electrical current through the alloys. In recovering their shape the metal alloys can produce a displacement or a force, or a combination of a displacement and a force, as a function of temperature. Shape-memory alloys have been exploited in mechanical and electrical mechanical control systems in order to provide a precise mechanical response to an electrically-induced temperature change.
Shape-memory alloys are discussed in the in Scientific American, Vol. 241 No. 5 pp. 74-82 (November 1979). The metals are also discussed in the article Shape Memory Affect Alloys for Robotic Devices by the same Schetky appearing in ROBOTICS AGE, July, 1984, pp. 13-17.
Shape-memory alloys are available from Memory Metals, Inc., 83 Keiler Avenue, Norwalk, Conn. 06854, and from other suppliers. Memory Metals, Inc. offers, under the Memrytec.TM. trademark, two-way memory alloy devices. In these devices, the shape-memory alloy returns to a "memorized shape" on both heating and cooling, and not just upon heating. Both two-way shape memory alloys, and standard one-way shape memory alloys, may commonly be formed as springs.